Abstract:

A distortion evaluating apparatus which can quantitatively evaluate
distortion in a measurement object surface is provided. A distortion
evaluating apparatus evaluates distortion based on three-dimensional
measurement data obtained from a measurement object surface. The
apparatus includes a secondary differential component adapted for
effecting a secondary differential operation on two-dimensional
measurement data of a cross section of the measurement object surface
indicative of unevenness therein, thus obtaining curvature data of the
cross section, a permissible range setting component adapted for setting
a permissible range for the curvature data, based on range of an upper
limit value and a lower limit value from a reference value, and a
distortion data extracting component adapted for extracting a portion of
the curvature data exceeding the set permissible range as distortion data
indicative of the distortion in the cross section.

Claims:

1. A distortion evaluating apparatus for evaluating distortion based on
three-dimensional measurement data obtained from a measurement object
surface, the apparatus comprising:a secondary differential component
adapted for effecting a secondary differential operation on
two-dimensional measurement data of a cross section of the measurement
object surface indicative of unevenness therein, thus obtaining curvature
data of the cross section;a permissible range setting component adapted
for setting a permissible range for said curvature data, based on range
of an upper limit value and a lower limit value from a reference value;
anda distortion data extracting component adapted for extracting a
portion of said curvature data exceeding said set permissible range as
distortion data indicative of the distortion in the cross section.

2. The distortion evaluating apparatus according to claim 1, wherein said
permissible range setting component changes at least one of said
reference value, said upper limit value and said lower limit value, in
accordance with a characteristics of said measurement object surface.

3. The distortion evaluating apparatus according to claim 1, wherein said
secondary differential component extracts said curvature data for each
one of a plurality of cross sections over said measurement object surface
three-dimensionally;said distortion data extracting component includes a
distortion degree evaluating component adapted for extracting said
distortion data for each one of said cross sections three-dimensionally;
andsaid distortion evaluating apparatus further comprises a distortion
degree evaluating component adapted for evaluating a degree of distortion
in a specific distorted region present in said measurement object
surface, based on said three dimensional distortion data.

4. The distortion evaluating apparatus according to claim 3, further
comprising:a distortion length extracting component adapted for
extracting the length of said specific distorted region based on three
dimensional distortion data;a distortion volume extracting component
adapted for extracting the volume of said specific distorted region based
on the three dimensional distortion data; andwherein said distortion
degree evaluating component evaluates the degree of distortion in the
specific distorted region by using the combination of the length and the
volume of the specific distorted region as distortion evaluation data and
comparing evaluation reference data and the distortion evaluation data
with each other.

5. The distortion evaluating apparatus according to claim 3, further
comprising:a distortion length extracting component adapted for
extracting the length of said specific distorted region based on three
dimensional distortion data;a distortion area extracting component
adapted for extracting the area of said specific distorted region based
on the three dimensional distortion data by integrating widths of the
specific distorted region perpendicular to the length along the direction
of this length; andwherein said distortion degree evaluating component
evaluates the degree of distortion in the specific distorted region by
using the combination of said length and said area of the specific
distorted region as distortion evaluation data and comparing evaluation
reference data and said distortion evaluation data with each other.

6. A distortion evaluating method for evaluating distortion based on
three-dimensional measurement data obtained from a measurement object
surface, the method comprising the steps of:effecting a secondary
differential operation on two-dimensional measurement data of a cross
section of the measurement object surface indicative of unevenness
therein, thus obtaining curvature data of the cross section;setting a
permissible range for said curvature data, based on a range of an upper
limit value and a lower limit value from a reference value; andextracting
a portion of said curvature data exceeding said set permissible range as
distortion data indicative of the distortion in the cross section.

Description:

TECHNICAL FIELD

[0001]The present invention relates to an apparatus and a method for
evaluating distortion based on three-dimensional measurement data
obtained from a measurement object surface.

BACKGROUND ART

[0002]In a body surface such as a surface of a door panel of a motorcar
manufactured with using a steel plate, there sometimes can develop a
shape different from an originally designed shape (i.e. distortion), due
to the thickness and/or composition of the steel plate used. And,
determination of whether the distortion is within an acceptable range or
not is effected through sensory evaluation by a skilled artisan. However,
this determination cannot be made appropriately under a predetermined
standard, unless the artisan is an experienced one who has actually
observed various distortions. For this reason, there has been proposed a
distortion evaluating apparatus designed to extract mechanically a
certain characteristics from the distortion in the measurement object
surface such as a body surface, thereby effecting the sensory evaluation
of distortion degree in a quantitative manner.

[0003]According to a technique employed by a distortion evaluating
apparatus described in Patent Document 1, a secondary differential
operation is carried out on two-dimensional measurement data of a cross
section of the measurement object surface, indicative of unevenness of
the surface and then e.g. a difference value between the maximum value
and the minimum value of the secondary differential values, as the
characteristics indicative of the distortion. Thereafter, this difference
value is assigned into a prediction formula, by which a distortion
evaluation value is predicted. More particularly, a difference between a
cross section shape line of the measurement object surface actually
determined and an ideal curve of values which comprise e.g. design data
per se is calculated, thus obtaining a surface distortion line including
all large and small distortions which have developed in the measurement
object surface. Then, a secondary differential operation is effected on
this surface distortion line obtained with including all large and small
distortions, and a difference value between the maximum value and the
minimum value of the resultant secondary differential values is utilized
for the distortion evaluation. The secondary differential values of this
two-dimensional measurement data (surface distortion line) correspond to
curvature data of the cross section of the measurement object surface.
And, it may be determined that the greater the absolute value of the
secondary differential value, the greater the distortion.

[0004]Patent Document 1: Japanese Patent No. 3015615

DISCLOSURE OF THE INVENTION

Problem to be Solved by Invention

[0005]According to the distortion evaluating apparatus described in Patent
Document 1, the apparatus employs a difference value between the maximum
value and the minimum value of two-dimensional measurement data, as a
characteristics used for distortion degree evaluation. This means that
the apparatus employs data including all, i.e. large and small
distortions present in the measurement object surface, for the purpose of
distortion evaluation of the measurement object surface. In the case of a
sensory evaluation by a human, on the other hand, even when a distortion
exists, this may sometimes be determined as permissible if it is not
conspicuous. On the other hand, in the case of the conventional method
using the secondary differential values of two-dimensional measurement
data as they are, without effecting any data processing thereon, the
method is configured to take note of and find problematic even such small
distortion also which would be found permissible by a sensory evaluation
by a human.

[0006]Further, if the absolute value of a secondary differential value is
large, this should be determined appropriately as being indicative of a
large distortion. However, such appropriate evaluation may sometimes be
not done by the distortion evaluating apparatus disclosed in Patent
Document 1. For instance, a certain waveform can have a large peak
(maximum value) of absolute value in the positive direction and has a
small peak (minimum value) of absolute value in the negative direction.
Another waveform can have equal peaks (maximum value and minimum value)
of absolute value in the positive direction and negative direction. Still
another waveform can have a small peak (minimum value) of absolute value
in the positive direction and has a large peak (maximum value) of
absolute value in the negative direction. In such case, the distortion
evaluating apparatus described in Patent Document 1 would provide a same
distortion evaluation result for all of these three kinds of waveforms as
long as the difference value between the maximum value and the minimum
value of the secondary differential values is the same.

[0007]Therefore, the distortion evaluation result obtained by the
conventional distortion evaluating apparatus would be different from the
desirable result which could be obtained by the human sensory evaluation.
Hence, it cannot be said that this conventional apparatus really effects
quantitative evaluation of distortion in a measurement object surface.

[0008]Moreover, the original shape of the measurement object surface to be
used as the baseline can sometimes be deformed by the spring-back
phenomenon of the steel plate, so that the cross section line obtained
therefrom may deviate from the design data. In this case, the
conventional method would determine such original shape of the
measurement object surface too as "distortion", which actually is not.
More particularly, the distortion evaluating apparatus disclosed in
Patent Document 1 is configured to attempt to calculate difference values
between a cross section shape line and an ideal curve so as to obtain a
surface distortion line which includes only the distortions which have
developed in the measurement object surface. As a matter of fact, the
above difference values include not only the distortions, but also the
original shape of the measurement object surface. Moreover, even if no
distortion has actually developed, there is the possibility of the
original shape of the measurement object surface formed by the spring
back being determined as a distortion erroneously.

[0009]In addition, in the case of the distortion evaluating apparatus
described in Patent Document 1, the apparatus monitors the secondary
differential values and calculates a difference value between the maximum
and minimum values thereof. Hence, there is another problem of the
apparatus being constantly under a computational load over a
predetermined level.

[0010]The present invention has been made in view of the above-described
problem. And, its object is to provide an apparatus and a method for
evaluating distortion which can quantitatively evaluate distortion in a
measurement object surface.

Means to Solve the Problem

[0011]According to a characterizing construction of a distortion
evaluating apparatus relating to the present invention for accomplishing
the above-noted object, a distortion evaluating apparatus for evaluating
distortion based on three-dimensional measurement data obtained from a
measurement object surface, the apparatus comprises:

[0013]permissible range setting means for setting a permissible range for
said curvature data, based on range of an upper limit value and a lower
limit value from a reference value; and

[0014]distortion data extracting means for extracting a portion of said
curvature data exceeding said set permissible range as distortion data
indicative of the distortion in the cross section.

[0015]In the above, the curvature data of the cross section refer to data
obtained by first effecting a differential operation on the two-dimension
measurement data of the cross section thus obtaining slope data for each
point of the cross section and then effecting a secondary differential
operation on the slope data for each point of the cross section, so that
the resultant data may indicate a change in the slopes of the cross
section. For example, in the case of a cross section with a fixed
curvature, such as a circle, the slope of the cross section changes by a
fixed amount, so that the slope change amount of each point of the cross
section will be constant. Whereas, in the case of a cross section with a
plurality of different curvatures, such as a sine waveform, the slope
change amount for each point in the cross section is not constant. As
described above, the secondary differential means extracts the curvature
data of the cross section by effecting a secondary differential operation
on the two dimension measurement data of a predetermined cross section
indicative of unevenness therein.

[0016]According to the above-described characterizing construction, the
secondary differential means effects a secondary differential operation
on two-dimensional measurement data of a cross section of the measurement
object surface indicative of unevenness therein, thus obtaining curvature
data of the cross section. The permissible range setting means sets a
permissible range for said curvature data, based on range of an upper
limit value and a lower limit value from a reference value. The
distortion data extracting means extracts a portion of said curvature
data exceeding said set permissible range as distortion data indicative
of the distortion in the cross section. That is to say, the distortion
evaluating apparatus having the above-described characterizing feature
effects a data processing operation which does not determine curvature
data with small absolute values within the set permissible range as any
distortion. This data processing operation is identical to the
above-described human sensory evaluation which disregards small
distortions.

[0017]Further, as the permissible range setting means sets the permissible
range for the curvature data, based on a range of an upper limit value
and a lower limit value from a reference value, it is possible to set
desirably which portion of the curvature data to be extracted as the
distortion data. That is to say, even when the original shape of the
measurement object surface has been deformed due to a spring back of the
steel plate, by appropriately increasing/decreasing the reference value
corresponding to the original shape in accordance with the deformed shape
so that the increased/decreased reference value may be substantially
equal to the secondary differential value of the cross section indicative
of the original shape, it is possible not to erroneously determine the
originally deformed shape due to the spring back as distortion.

[0018]In addition, as the distortion data extracting means is to effect
only the comparison between the set permissible range with the curvature
data in order to extract the distortion data, no significant
computational load will be applied to the distortion evaluating
apparatus.

[0019]As described above, the distortion data on which the inventive
distortion evaluating apparatus effects the distortion evaluation is
analogous to information on which a human worker effects his/her sensory
evaluation. Hence, distortion in a measurement object surface can be
evaluated quantitatively.

[0020]According to a further characterizing construction of the distortion
evaluating apparatus relating to the present invention, said permissible
range setting means changes at least one of said reference value, said
upper limit value and said lower limit value, in accordance with a
characteristics of said measurement object surface.

[0021]If the measurement object surface is flat, then, the secondary
differential value of its cross section will be zero (the curvature data
of the cross section will be zero). Whereas, if the cross section shape
of the measurement object surface is curved originally, the curvature
data of the cross section indicative of this cross section shape may
exceed the set permissible range. In such case, even in the absence of
any distortion, the curvature data of the cross section indicative of the
original shape of the measurement object surface may be determined as
distortion data erroneously.

[0022]Then, according to the above-described characterizing construction,
as the permissible range setting means changes at least one of said
reference value, said upper limit value and said lower limit value, in
accordance with a characteristics of said measurement object surface,
distortion which has actually developed in the measurement object surface
can be extracted as distortion data selectively. As a result, distortion
in a measurement object surface can be evaluated quantitatively.

[0023]According to a still further characterizing construction of the
distortion evaluating apparatus relating to the present invention, said
secondary differential means extracts said curvature data for each one of
a plurality of cross sections over said measurement object surface
three-dimensionally;

[0024]said distortion data extracting means includes distortion degree
evaluating means for extracting said distortion data for each one of said
cross sections three-dimensionally; and

[0025]said distortion evaluating apparatus further comprises a distortion
degree evaluating means for evaluating a degree of distortion in a
specific distorted region present in said measurement object surface,
based on said three dimensional distortion data.

[0026]According to the above-described characterizing construction, as the
distortion degree evaluating means evaluates a degree of distortion in a
specific distorted region present in said measurement object surface,
based on said three dimensional distortion data, it is possible to
determine quantitatively a degree of distortion included in the three
dimensional shape of the measurement object surface.

[0027]According to a still further characterizing construction of the
distortion evaluating apparatus relating to the present invention, the
apparatus further comprises a distortion length extracting means for
extracting the length of said specific distorted region based on three
dimensional distortion data and a distortion volume extracting means for
extracting the volume of said specific distorted region based on the
three dimensional distortion data; and said distortion degree evaluating
means evaluates the degree of distortion in the specific distorted region
by using the combination of the length and the volume of the specific
distorted region as distortion evaluation data and comparing evaluation
reference data and the distortion evaluation data with each other.

[0028]According to the above-described characterizing construction, the
distortion length extracting means extracts the length of said specific
distorted region based on the three dimensional distortion data and the
distortion volume extracting means extracts the volume of said specific
distorted region based on the three dimensional distortion data. And, the
distortion degree evaluating means evaluates the degree of distortion in
the specific distorted region by using the combination of the length and
the volume of the specific distorted region as distortion evaluation data
and comparing evaluation reference data and the distortion evaluation
data with each other. Therefore, it is possible to determine
quantitatively a degree of distortion included in the three dimensional
shape of the measurement object surface, with using the characteristics
(length and volume of the distorted region) included in the three
dimensional distortion data of the measurement object surface.

[0029]According to a still further characterizing construction of the
distortion evaluating apparatus relating to the present invention, the
apparatus further comprises a distortion length extracting means for
extracting the length of said specific distorted region based on three
dimensional distortion data and a distortion area extracting means for
extracting the area of said specific distorted region based on the three
dimensional distortion data by integrating widths of the specific
distorted region perpendicular to the length along the direction of this
length; and said distortion degree evaluating means evaluates the degree
of distortion in the specific distorted region by using the combination
of said length and said area of the specific distorted region as
distortion evaluation data and comparing evaluation reference data and
said distortion evaluation data with each other.

[0030]According to the above-described characterizing construction, the
distortion length extracting means extracts the length of said specific
distorted region based on three dimensional distortion data and the
distortion area extracting means extracts the area of said specific
distorted region based on the three dimensional distortion data by
integrating widths of the specific distorted region perpendicular to the
length along the direction of this length. Then, the distortion degree
evaluating means evaluates the degree of distortion in the specific
distorted region by using the combination of said length and said area of
the specific distorted region as distortion evaluation data and comparing
evaluation reference data and the distortion evaluation data with each
other. Therefore, it is possible to determine quantitatively a degree of
distortion included in the three dimensional shape of the measurement
object surface, with using the characteristics (length and area of the
distorted region) included in the three dimensional distortion data of
the measurement object surface.

[0031]According to a characterizing feature of a distortion evaluating
method relating to the present invention for accomplishing the
above-noted object, a distortion evaluating method for evaluating
distortion based on three-dimensional measurement data obtained from a
measurement object surface, the method comprises the steps of:

[0032]effecting a secondary differential operation on two-dimensional
measurement data of a cross section of the measurement object surface
indicative of unevenness therein, thus obtaining curvature data of the
cross section;

[0033]setting a permissible range for said curvature data, based on a
range of an upper limit value and a lower limit value from a reference
value; and

[0034]extracting a portion of said curvature data exceeding said set
permissible range as distortion data indicative of the distortion in the
cross section.

[0035]According to the above-described characterizing feature, a secondary
differential operation is effected on two-dimensional measurement data of
a cross section of the measurement object surface indicative of
unevenness therein, thus obtaining curvature data of the cross section.
The method sets a permissible range for said curvature data, based on a
range of an upper limit value and a lower limit value from a reference
value. Then, a portion of said curvature data exceeding said set
permissible range is extracted as distortion data indicative of the
distortion in the cross section. That is to say, the distortion
evaluating method having the above-described characterizing feature
effects a data processing operation which does not determine curvature
data with small absolute values within the set permissible range as any
distortion. This data processing operation is identical to the human
sensory evaluation which disregards small distortions.

[0036]Further, as the method sets the permissible range for the curvature
data, based on a range of an upper limit value and a lower limit value
from a reference value, it is possible to set desirably which portion of
the curvature data is to be extracted as the distortion data. That is to
say, even when the original shape of the measurement object surface has
been deformed due to a spring back of the steel plate, by appropriately
increasing/decreasing the reference value corresponding to the original
shape in accordance with the deformed shape so that the
increased/decreased reference value may be substantially equal to the
secondary differential value of the cross section indicative of the
original shape, it is possible not to erroneously determine the
originally deformed shape due to the spring back as distortion.

[0037]In addition, as the distortion data extraction involves only the
comparison between the set permissible range with the curvature data for
extracting the distortion data, there occurs no significant computational
load.

[0038]As described above, the distortion data on which the inventive
distortion evaluating method effects the distortion evaluation is
analogous to information on which a human effects his/her sensory
evaluation. Hence, distortion in a measurement object surface can be
evaluated quantitatively.

BEST MODE OF EMBODYING THE INVENTION

First Embodiment

[0039]FIG. 1 shows a functional block diagram of a non-contact, three
dimensional measurement system and a distortion evaluating apparatus 40
relating to a first embodiment of the present invention. This non-contact
three dimensional measurement system is used for effecting non-contact,
three-dimensional measurement of a shape of a door panel manufactured by
press-working a steel plate in a mold. And, this three-dimensional
measurement system includes a robot hand 10 as a measuring head moving
means, a non-contact three-dimensional measuring means 20 for effecting
checkered pattern analysis of a grating pattern photographic image
projected on a measurement object surface while being shifted in phase
under a tracking scanning of the door panel by the robot hand 10, thus
obtaining three dimensional coordinate values for each pixel of the
imaging image and outputting a measurement image with three dimensional
distance data assigned to respective pixels thereof (More precisely,
values of pixels constituting the image comprise the three dimensional
distance data. Therefore, this image is different from an ordinary image,
but will be referred to herein as "measurement image" for facilitating
understanding), and a three dimensional measurement control unit 30 for
processing measurement images of respective portions of the door panel
transferred one after another from the non-contact three dimensional
measuring means 20 and then generating three dimensional measurement data
of the entire door panel. Also, the distortion evaluating apparatus 40
can be realized by combination of an arithmetic processing unit such as a
computer and a predetermined program.

[0040]The robot hand 10 per se is a known device consisting essentially of
an arm mechanism 11 having, at a leading end thereof a tool attaching
portion 11a which is movable three-dimensionally and a robot hand
controller 12 for controlling the movements of this arm mechanism 11.

[0041]The non-contact three dimensional measuring means 20 includes a
measuring head 21 having a checkered pattern projecting portion 21a
acting as a projector for projecting a grating pattern onto a measurement
object surface and a camera portion 21b for imaging a grating image which
is deformed as being projected on the measurement object surface, a
control portion 22 for controlling the checkered pattern projecting
portion 21a, the camera portion 21b, etc. and a three dimensional
distance data measuring portion 23 for analyzing the image transmitted
from the camera portion 21b and then generating and outputting the
above-described measurement image. With such non-contact three
dimensional measuring means 20, high precision measurement is made
possible by combining the grating pattern projection with phase shift
technique. The measuring principle and construction thereof are known and
described in e.g. Japanese Patent Application "Kokai" No. 2004-317495 and
Japanese Patent Application "Kokai" No. 2002-257528. As the measuring
head 21 is attached to the tool attaching portion 11a of the robot hand
10, the measuring head 21 can be moved to a desired position for
effecting the three dimensional measurement.

[0042]Now, an explanation will be made with reference to FIG. 2 on the
photographic image obtained by the camera portion 21b and the measurement
image corresponding to this photographic image. The photographic image
shows a deformed grating pattern formed as the grating pattern projected
onto the measurement object surface by the checkered pattern projecting
portion 21a is deformed due to shape change or curvature of the
measurement object surface, the deformed grating pattern being shown as
density variations which are pixel values of respective pixels
constituting this photographic image. Then, by effecting an image
analysis of the deformed grating pattern of this photographic image which
varies according to variation in the shape of the measurement object
surface, there are obtained three dimensional coordinate values of the
respective pixel (this need not necessarily have one-to-one relationship
with the pixel of the photographic image), that is, the three dimensional
distance data. The data comprising the three dimensional distance data
assigned instead of the density as the pixel value of each pixel is
referred to as "measurement image" herein. For instance, a certain pixel
Pn of the measurement image is to have three dimensional coordinate
values (three dimensional distance data) as (Xn, Yn, Zn).

[0043]The three dimensional measurement data generated as above is then
transferred from the three dimensional measurement control unit 30 to the
distortion evaluating apparatus 40. Next, the construction of this
distortion evaluating apparatus 40 and the distortion evaluating method
effected with using the distortion evaluating apparatus 40 will be
described.

[0044]As shown in FIG. 1, the distortion evaluating apparatus 40 includes
a secondary differential means 41 for effecting a secondary differential
operation on two-dimensional measurement data of a predetermined cross
section of the measurement object surface indicative of unevenness
therein, thus obtaining curvature data of the cross section, a
permissible range setting means 43 for setting a permissible range for
the curvature data, based on a range of an upper limit value and a lower
limit value from a reference value, and a distortion data extracting
means 42 for extracting a portion of the curvature data exceeding said
set permissible range as distortion data indicative of the distortion in
the cross section. The secondary differential means 41 obtains the
curvature data of a plurality of respective cross sections over the
measurement object surface three dimensionally.

[0045]As described above, the secondary differential means 41 is used for
obtaining curvature data of cross sections. More particularly, when a
differential operation is effected on two dimensional measurement data of
a cross section, there is obtained slope data for each point in the cross
section. Further, when a further differential operation is effected on
this slope data for each point of the cross section, there is obtained
slope change data. For example, in the case of a cross section with a
fixed curvature, such as a circle, the slope of the cross section changes
by a fixed amount, so that the slope change amount of each point of the
cross section will be constant. Whereas, in the case of a cross section
with a plurality of curvatures, such as a sine waveform, the slope change
amount for each point in the cross section is not constant. As described
above, it may be said that the secondary differential means 41 extracts
the curvature data of the cross section by effecting a secondary
differential operation on the two dimension measurement data of a
predetermined cross section indicative of unevenness therein.

[0046]FIG. 3 shows distortion data to be described later in a grey scale
corresponding to the magnitudes of values thereof. More particularly, the
cross section curvature data obtained by the secondary differential means
41 are drawn three dimensionally for a plurality of mutually parallel
cross sections of the measurement object surface. In this embodiment, a
door handle attaching portion 2 is used as an example of the measurement
object surface. As shown in FIG. 3, the door handle attaching portion 2
is laid laterally and there are developed distorted regions G1 through G4
at total four positions, i.e. at right and left ends and upper and lower
positions of the attaching portion 2. FIG. 4 (a) shows a graph including
a shape line (shown by a dot line) of a cross section A-A' at a position
distant by a distance (a) in an upper direction (positive direction along
the L-axis) from the door handle attaching portion 2 and curvature data
(shown by a solid line) obtained as the result of the secondary
differential operation on the two dimensional measurement data thereof.
And, FIG. 4 (b) shows a graph including a shape line (shown by a dot
line) of a cross section B-B' at a position distant by a distance (b) in
the upper direction (positive direction along the L-axis) from the door
handle attaching portion 2 and curvature data (shown by a solid line)
obtained as the result of the secondary differential operation on the two
dimensional measurement data thereof. In this, in FIG. 4, the respective
curvature data comprises data (1/ρ) obtained by multiplying the data
obtained by the secondary differential of the two dimensional measurement
data of the cross section, with a value of "-1". And, "ρ" is the
radius of the circumference forming the cross section. As described
above, in this embodiment, since the values obtained by the secondary
differential operation on the two dimensional measurement data are
multiplied with the value "-1", if the cross section has an upwardly
convex shape, the curvature of the portion of the cross section
corresponding thereto will appear as an upwardly convex shape.
Conversely, if the cross section has a downwardly convex shape, the
curvature of the portion of the cross section corresponding thereto will
appear as a downwardly convex shape correspondingly.

[0047]FIG. 4 shows also the set permissible range for the curvature data.
This set permissible range is set by the permissible range setting means
43 as a range between an upper limit value and a lower limit value
relative to a predetermined reference value. This set permissible range
is used for extracting, from the above-described curvature data,
distortion data indicative of distortion in the cross section.

[0048]The reference value is set, based on the original cross section
shape of the measurement object surface. That is, the reference value can
be a secondary differential value obtained by effecting a secondary
differential operation on a cross section of the measurement object
surface which is still free from any distortion. In this particular
embodiment, as the curvature of the original measurement object surface
of the attaching portion 2 is constant, the reference value is set as a
constant value (especially, if the measurement object surface is a flat
surface with zero curvature, the reference value can be set=0).
Therefore, if no distortion occurs in the measurement object surface, the
curvature data of the cross section will be equal to the reference value.

[0049]However, if a distortion develops in the measurement object surface,
this causes deviation of the curvature data of the cross section from the
reference value. More particularly, if a distortion with a small
curvature occurs in the measurement object surface (i.e. a distortion
with a gently varying slope at each point of the cross section), this
will appear as a small amount of deviation of the curvature data of the
cross section from the reference value. On the other hand, if a
distortion with a large curvature occurs in the measurement object
surface (i.e. a distortion with a sharply varying slope at each point of
the cross section), this will appear as a large amount of deviation of
the curvature data of the cross section from the reference value.
Therefore, a portion with curvature data thereof being within the set
permissible range can be determined not to be a distortion, whereas a
portion with curvature data thereof exceeding the set permissible range
can be determined to be a distortion.

[0050]That is, the distortion data extracting means 42 extracts, from
among the curvature data, data over the upper limit value and data below
the lower limit value as distortion data indicative of the distortion in
that cross section.

[0051]As described above, by determining, from among the curvature data,
data over the upper limit value and data below the lower limit value as
distortion data indicative of the distortion in that cross section, it is
possible to avoid extraction of unnecessary distortion data such as a too
small distortion (i.e. an invisible distortion with a very gentle slope
change at each point of the cross section).

[0052]And, a distortion degree evaluating means 46 evaluates a degree of
distortion in a specific distorted region present in the measurement
object surface, based on the three dimensional distortion data obtained
over the measurement object surface.

[0053]Next, this evaluation of a distortion degree of a predetermined
region in the measurement object surface effected by the distortion
degree evaluating means 46 will be described in greater details.

[0054]FIG. 3 shows distortion data extracted by the distortion data
extracting means 42 being shown in grey scale distribution according to
magnitudes of values thereof. This can be displayed by a display device
(not shown) connected to the distortion evaluating apparatus 40. That is,
this FIG. 3 shows values exceeding the set permissible range and values
below the set permissible range, from among the cross section curvature
data. And, in the instant embodiment, as shown, there are developed the
total of four distorted regions G1-G4 in the periphery of the attaching
portion 2. And, in this embodiment, the width extension of the distorted
region along the direction normal to each cross section (L-axis
direction) is defined as a distortion length: L (FIG. 3 shows the
distortion length L1 of the distorted region G1). A distortion length
extracting means 44 is provided for automatically extracting the
respective length of the specific distorted region such as the regions G1
through G4 described above, based on the three dimensional distortion
data extracted by the distortion data extracting means 42.

[0055]FIG. 5 is a graph schematically showing curvature data for a
plurality of respective cross sections and the upper limit values of the
above-described set permissible range. Of the curvature data of the
respective cross sections shown in FIG. 5, the data exceeding the upper
limit values are the distortion data. And, the region exceeding the upper
limit value for each cross section will be referred to as a cross
sectional area: S1. Therefore, a region where a plurality of such cross
sectional areas: S1 are present will be determined as a distorted region:
Ga, Gb.

[0056]Then, a distortion volume extracting means 45 extracts the volume of
each distorted region: Ga, Gb by multiplying the cross sectional areas:
S1 for the respective cross sections over the distortion length L.

[0057]As described above, with use of the distortion length extracting
means 44 and the distortion volume extracting means 45, the length and
volume of a specific distorted region are extracted. And, with the
distortion evaluating apparatus 40 relating to this embodiment, the
distortion degree evaluating means 46 employs the combination of the
length and the volume of the specific distorted region as distortion
evaluation data and compares this distortion evaluation data with a
predetermined evaluation reference data, thus evaluating the degree of
the specific distortion. This evaluation reference data can be obtained
empirically by comparing result of a human sensory evaluation on a
specific distorted region and the distortion evaluation data comprising
the length and the volume of the distorted region obtained according to
the present embodiment as above.

[0058]FIG. 6 is a graph showing such result of comparison between the
distortion evaluation data and evaluation reference data, plotting
altogether distortion evaluation data extracted for 10 (ten) distorted
regions by the distortion evaluating apparatus 40 of the invention. This
graph showing comparison result can be displayed on a display device (not
shown) to be connected to the distortion evaluating apparatus 40. In FIG.
6, the horizontal axis represents the distortion length whereas the
vertical axis represents the distortion volume. And, for these ten (10)
distorted regions, human sensory evaluations were carried out
respectively therefor. And, the results of the sensory evaluations (from
five points (good) to one point (poor)) are indicated with using
different markers for the plottings thereof.

[0059]As shown in FIG. 6, with the distortion evaluating apparatus 40 of
the present invention, the evaluation reference data are set such that
the longer the distortion length and the greater the distortion volume,
the lower (poorer) the evaluation of the degree of distortion in the
distorted region. In FIG. 6, for the three distorted regions for which
the human sensory evaluations provided poor results (from one to two
points), similarly poor evaluation results were provided by the inventive
distortion evaluating apparatus 40 also. On the other hand, for the seven
distorted regions for which the human sensory evaluations provided good
results (from three to five points), similarly good evaluation results
were provided by the inventive distortion evaluating apparatus 40 also.

[0060]That is to say, with the distortion evaluating apparatus 40 of the
present invention, the distortion degree evaluation effected by the
distortion degree evaluating means 46 by using the combination of the
length (i.e. the width extension of the distorted region) and the volume
(i.e. the strength of the distorted region) as the distortion evaluation
data and making comparison between this distortion evaluation data with
the predetermined evaluation reference data is found to be consistent
with the human sensory evaluation result.

[0061]As described above, the distortion evaluating apparatus 40 relating
to the present embodiment effects a data processing operation which does
not interpret curvature data with a small absolute value within a set
permissible range as a distortion. And, this data processing is
substantially equivalent to a sensory evaluation made by a human who
finds a small distortion as permissible. That is to say, the
above-described distortion data on which the result of distortion
evaluation by the distortion evaluating apparatus 40 of this embodiment
is based is analogous to the information on which the result of the human
sensory evaluation is based.

[0062]Therefore, it may be said that a result of evaluation of distortion
degree conventionally relied on a human sensor evaluation by a skilled
artisan can now be quantitatively obtained by the distortion evaluating
apparatus 40 of the present embodiment. Namely, a distortion which
requires correction can be easily determined under a certain constant
standard, whereby unnecessary distortion correction or unnecessary
repetition of distortion correction can be avoided advantageously.
Further, with using the distortion evaluating apparatus 40, a distortion
which has developed on a body surface (e.g. a door panel surface of a
motorcar) manufactured by press working can be discovered properly under
the predetermined standard. Therefore, it is possible to make an
appropriate correction on the mold used for this press working operation
so as not to develop any distortion thereafter. That is, the distortion
evaluating apparatus 40 of the invention can be utilized also for
inspection of a mold to be used in press working.

[0063]Further, when an un-experienced human worker effects a sensory
evaluation based on his/her sense, it is possible for this worker to make
reference to the result of distortion evaluation quantitatively obtained
by the distortion evaluating apparatus 40 which is equivalent to the
result of human sensory evaluation made by an experienced artisan. That
is to say, there is obtained a further advantage of providing the
possibility of making reference to the quantitative evaluation result
obtained by the distortion evaluating apparatus 40 for the purpose of
allowing a less-skilled worker to develop his/her sensor skill so as to
be able to obtain improved evaluation result.

Second Embodiment

[0064]A distortion evaluating apparatus 50 relating to the second
embodiment differs from that the first embodiment in that the distortion
degree evaluating means 46 employs the combination of the length and the
area of a specific distorted region as the distortion evaluation data.
Next, the distortion evaluating apparatus 50 according to the second
embodiment will be described. The following discussion, however, will
omit discussion of same or substantially same constructions as those of
the first embodiment.

[0065]FIG. 7 shows a functional block diagram of the non-contact, three
dimensional measurement system and distortion evaluating apparatus 50
relating to the second embodiment. The distortion evaluating apparatus 50
according to this second embodiment includes a distortion area extracting
means 47 for extracting the area of a specific distorted region, and the
distortion degree evaluating means 46 employs the combination of the
length and the area of the specific distorted region as the distortion
evaluation data and effects comparison between this distortion evaluation
data and the evaluation reference data for evaluating the degree of
distortion in the specific distorted region.

[0066]Like FIG. 5 described hereinbefore, FIG. 8 is a graph schematically
showing curvature data for a plurality of respective cross sections and
the upper limit value of the above-described set permissible range. There
is shown a length of the portions intersecting with the upper limit
value, i.e. a width: W of the distorted region. Then, the distortion area
extracting means 47 obtains the area S2 of this specific distorted region
by integrating the widths: W of the specific distorted region
perpendicular to the length along the length direction (L-axis
direction), based on the three dimensional distortion data extracted by
the distortion data extracting means 42.

[0067]And, the distortion degree evaluating means 46 employs the
combination of the length and the area of the specific distorted region
as distortion evaluation data and compares this distortion evaluation
data with a predetermined evaluation reference data, thus evaluating the
degree of the specific distortion. FIG. 9 is a graph showing such result
of comparison between the distortion evaluation data and evaluation
reference data, plotting altogether distortion evaluation data extracted
for 10 (ten) distorted regions by the distortion evaluating apparatus 50
of the invention. In FIG. 9, the horizontal axis represents the
distortion length whereas the vertical axis represents the distortion
area. And, for these ten (10) distorted regions, human sensory
evaluations were carried out respectively therefor. And, the results of
the sensory evaluations (from five points (good) to one point (poor)) are
indicated with using different markers for the plottings thereof.

[0068]As shown in FIG. 9, with the distortion evaluating apparatus 50 of
the present embodiment, like the first embodiment described above, the
evaluation reference data are set such that the longer the distortion
length and the greater the distortion area, the lower (poorer) the
evaluation of the degree of distortion in the distorted region. The
evaluation reference data can be obtained empirically by comparing the
result of a human sensory evaluation on a specific distorted region and
the distortion evaluation data comprising the length and the area of the
distorted region obtained according to the present embodiment as above.

[0069]In FIG. 9, for the three distorted regions for which the human
sensory evaluations provided poor results (from one to two points),
similarly poor evaluation results were provided by the inventive
distortion evaluating apparatus 50 also. On the other hand, for the seven
distorted regions for which the human sensory evaluations provided good
results (from three to five points), similarly good evaluation results
were provided by the inventive distortion evaluating apparatus 50 also.
That is to say, the distortion degree evaluation effected by the
distortion degree evaluating means 46 of the inventive distortion
evaluating apparatus 50 is found to be consistent with the human sensory
evaluation result.

Other Embodiments

[0070]<1>

[0071]In the foregoing embodiments, the permissible range setting means 43
can variably set the reference value, the upper limit value and the lower
limit value as desired. For instance, in FIG. 10 (a) shows an example
setting in which of the set permissible range shown in FIG. 4 (a), the
upper limit value is changed. For example, even if a distortion exists in
the measurement object surface, if this exists at an inconspicuous part
(e.g. a part where the cross section shape of the original measurement
object surface is flat), the upper limit value and the lower limit value
can be set smaller so as to allow even small curvature data to be
extracted as distortion data.

[0072]Further, FIG. 10 (b) shows another example setting in which of the
set permissible range shown in FIG. 4 (b), the reference value of a
specific portion of the measurement object surface is changed. More
particularly, the reference value is partially reduced. In this way, not
only the upper limit value and the lower limit value, the reference value
too can be changed. For instance, in case the curvature data is not zero
as the original cross section shape of the measurement object surface is
not flat, but curved, the secondary differential data (curvature data) of
the original cross section shape of the measurement object surface can be
set as the reference value.

[0073]As described above, the reference value, the upper limit value and
the lower limit value can be set variably as desired, in accordance with
various characteristics such as the designed original cross section shape
of the measurement object surface.

<2>

[0074]In the foregoing embodiments, as shown in FIG. 6 and FIG. 9,
respectively, with comparison between the distortion evaluation data and
one evaluation reference data, the degree of distortion in a specific
distorted region is evaluated in the two steps of "good" and "poor".
Instead of this, the distortion evaluation data can be compared with a
plurality of evaluation reference data set in a plurality of steps. And,
the degree of distortion in a specific distorted region can be evaluated
in a greater number of steps. For example, if two evaluation reference
data are provided, another curve of the same shape as the evaluation
reference data shown in FIG. 6 and FIG. 9 can be set in juxtaposition so
as not to intersect with each other. With this, the degree of distortion
of a specific distorted region can be evaluated in three steps of:
"good", "acceptable" and "poor".

INDUSTRIAL APPLICABILITY

[0075]The distortion evaluating apparatus according to the present
invention can utilized in quantitatively evaluating distortion in a body
surface of a vehicle such as a motorcar. Therefore, as distortion which
has developed in the body surface (e.g. a door panel surface of a
motorcar) manufactured by press working can be discovered appropriately
under a predetermined standard, it becomes possible to correct properly
the mold used for this press working so as not to develop distortion
thereafter. That is, the distortion evaluating apparatus of the invention
can be utilized also for inspection of a mold to be used for press
working.

[0076]Further, through accumulation of technique by repetition of such
steps as designing of body shape, designing of mold, press working,
distortion evaluation, correction of mold, it is possible to improve the
prediction technique including CAE (computer-aided engineering) in
designing a body shape and a mold which can effectively resist
development of distortions therein.

[0077]Moreover, by utilizing the fact that the evaluation result of
distortion degree is provided in the quantitative manner, the invention
can be utilized for determination of whether a sensory evaluation of
distortion degree by human sense is appropriate or not; that is, the
invention can be utilized for technique heritance for educating a
less-experienced human to a skilled artisan.

BRIEF DESCRIPTION OF THE DRAWINGS

[0078][FIG. 1] a functional block diagram of a non-contact, three
dimensional measurement system and a distortion evaluating apparatus
according to a first embodiment,

[0079][FIG. 2] an explanatory view of a photographic image obtained by a
measuring head and a measurement image obtained from this photographic
image,

[0081][FIG. 4] (a) a graph of a shape line at section A-A' in FIG. 3 and
data obtained by effecting secondary differential operation on its two
dimensional measurement data, (b) a graph of a shape line at section B-B'
in FIG. 3 and data obtained by effecting secondary differential operation
on its two dimensional measurement data,

[0082][FIG. 5] a graph schematically showing curvature data of a plurality
of respective cross sections and an upper limit value of a set
permissible range,

[0083][FIG. 6] a graph showing result of comparison between distortion
evaluation data comprising combination of a length and a volume of a
distorted region and evaluation reference data,

[0084][FIG. 7] a functional block diagram of a non-contact, three
dimensional measurement system and a distortion evaluating apparatus
according to a second embodiment,

[0085][FIG. 8] a graph schematically showing curvature data of a plurality
of respective cross sections and an upper limit value of a set
permissible range,

[0086][FIG. 9] a graph showing evaluation reference data for evaluating
distortion evaluation data comprising combination of a length and an area
of a distorted region, and

[0087][FIG. 10] graphs illustrating changes in the set permissible range.